Radio receiver control device



May 26, 1942. I G. w. THELIN I RADIO RECEIVER CONTROL DEVICE Filed Au 5, 1940 2 Sheets-Sheet 1 INVENTOR WILLARD THELIN TREB E FlG.l

May 26, 1942.

G. W. THELIN RADIO RECEIVER CONTROL DEVICE Filed Aug. 3,' 1940 2 Sheets-Sheet 2 -INVENTOR mu 7:324 m 4 5E8 AN curate calibration Patented May 26, 942

. RADIO RECEIVER'CONTROL DEVICE George Willard Thelin, Marion, Ind., assignor to Farnsworth. Television and Radio Corporation, a corporation of Delaware Application August 3, 1940, Serial No. 350,408

3 Claims. (01. 74-90) This invention relates to means for actuating variable control devices, and more particularly to a mechanism suitable for actuating a variable control of the type employed, for example, for I the regulation of tone or volume in a radio receiver.

In previously-known arrangements in which the shaft of the variable control was arranged parallel with the panel of the receiver, the control was actuated by means "of a disc mounted upon the control shaft and protruding through a slot in the panel. By contact withthe knurled edge of the disc, the operator could adjust the variable control. Calibration and manipulation of such prior-art devices were difiicult and unsatisfactory.

The present invention is directed to the problemof providing an improved means for actuating a variable control which is mounted with its shaft parallel to the panel of the receiver or other device, of which the control is acomponent part.

It is an object of the present invention'to provide an actuating mechanism for a variable control by means of which a substantially linear movement of a control knob produces positive rotation of the shaft of the variable control.

An additional object is toprovide an actuating mechanism for a variable control so arranged that the actuation may be performed by a motion functionally related to the efiect of the control upon a system to which it is connected.

Another object of the invention is to provide means whereby a relatively short movement of the control knob produces rotation of the variable control shaft through a relatively large number of degrees. V

A still further object of the invention is to provide positive means for indicating the setting of a variable control which is actuated by the linear movement of a knob, thus permitting acof the variable control if desired.

In accordance with the present invention, there is provided a variable-control actuating mechanism which includes a lever slidably pivoted ;at one end about an axis parallel to the shaft as to extend slightly over the scale l6 which is of the variable control. A first member is'mount- ,lever and its point of swivel is so proportioned,

with respect to the radius of the point of swivel on the second member, that the free end of the lever moves in a substantially straight line. Ad,-

ditionally, the first and second members are so proportioned that rotation of the lever about its pivot through relatively few degrees produces rotation of the variable-control shaft through relatively many degrees.

For a better understanding of the invention, together with other and further objects thereof,

reference is made to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a plan view, partly in section, of

a preferred form of the present invention;

Fig. 2 is an elevation, partly in section, taken on line 2-2 of Fig. 1;

Fig. 3 is a front view of a pair of control devices such as shown in Figs. 1 and 2; and

Fig. 4 is a circuit diagram, partlyv in block form, of a radio receiver incorporating two variable controls provided -with actuating mechanisms in accordance-with the invention. I

Referring now more particularly to Figs. 1 and 2 of the drawings, there is showna mounting bracket l which may be attached by any suitable means to the panel 2 of a radio receiver or the 'on its shaft ID a member lLsecured thereto.

The arcuately shaped member I2 is pivotally secured to the bracket 1 by means of the pin 13, and its periphery is adapted to engage the periphery of the member H. The lever 3 is swivelly connected to the member l2 by means of the pin l4. Apointer l5 may be provided, and is attached to the knob I in such a manner secured to the panel 2 in a position paralleling the slot 6, as more clearly shown in Fig. 3.

In operation, it will be apparent that the tendency of the knob I to move away from the front of the panel 2, as it moves toward the position indicated by dotted lines at 1A in Fig. 2, is substantially compensated by the movement of the pin 4, away from the back of the panel 2. As a result, the pointer l5 lies substantially the same distance away from the scale l6 whether the knob be in the position indicated at I, at 1A, or at 1B in Fig. 2.

smooth, at least one of the surfaces being of resilient material, so that their engagement depends entirely upon friction, without departing from the scope of the invention.

The scale It may be calibrated in arbitrary units as shown in Fig. 3, or other means may be employed instead of or in addition to arbitrary units, to indicaterthe effect of moving the knob upon the performance of the system in which the variable control is employed. If the variable control is used as a tone control,'for example, the scale IG may be provided with a music color scale to indicate visually the effect of the tone control. Other means for calibrating the scale I 6 will readily occur to those skilled in the art, and may be employed. without departing from the scope of the invention.

Referring to Fig. 4, there is shown a radio receiving system comprising an antenna II, a

high-frequency selector and amplifier It, a demodulator IS, a signal-repeating system 20, an

output audio-frequency amplifier H, a loud speaker 22, and a power supply 23. The signalrepeating system includes a vacuum tube 24, a volume control potentiometer 25, a bass tonecontrol rheostat 26, and a treble tone-control rheostat 21. .The rheostat 26 is shunted by a capacitor 28, and the Junction of the rheostat 26 and the capacitor 28 is connected to the. junction of the resistors 29 and 30 which are connected in series across a portion of the potentiometer 25. The rheostat 21 is connected in series with the capacitor 3| across the output terminals of the signal-repeating system 20.

It will be seen that the capacitor 28 and the resistor 29 are effectively in series across the potentiometer 25. .Due to the reactance of .the capacitor, the impedance of this shunting network increases with decreasing frequency, so that the signal voltage developed across the potentiometer 25, due to the substantially constant signal current from the demodulator I9, is greater at the lower audible frequencies than at the treble end of the musical scale. The effect of the capacitor 28 upon the frequency response may be varied by means'of the rheostat 26. When the slider is at its uppermost position, the capacitor 23 is short-circuited and the low-frequency response is at a minimum. As the slider.

is moved downward, the impedance of the shunt network 28-2! to low frequencies becomes increasingly greater, so the low-frequency response is increased. Since the capacitor 23 hasrelatively low reactance at the higher frequencies, the treble response remains substantially unchanged.

The function of the resistor 30 is to prevent the impedance of the network-2323 from rising too rapidly'as the frequency decreases. The

resistor 3| is'connected to a tap on the potentiometer 25, so that the low-frequency accentuation is more pronounced at low settings of the potentiometer 25, thus compensating in.

the well-known manner for the deficiency of the ear at the lower volume levels. 7

The high-frequency response of the system of this rheostat at its lowermost position,

the attenuation of the treble response due to the capacitor 3| is maximum. As the slider is moved upward, an increasing resistance is mserted in series with the capacitor 3|, so that its shunting effect is reduced and the treble response is increased. The value of the .capacitor 3| is sufiiciently small so that it has substantially no eflect upon the low-frequency response of the system regardless of the setting of the rheostat 21.

.In a preferred arrangement employing two controls in accordance with the invention, such as shown in Fig. 4, the bass tone control is preferably arranged to provide accentuation of the bass portion of the musical scale when its control knob is pushed downwardly, as indicated by the scale It of Fig. 3, and the treble tone control to increase the reproduction of high notes when its control knob is pushed upwardly as indicated by the scale NA of Fig. 3.

Although the mechanism in accordance with the present invention may be made in a number of different forms and proportions, in one successful embodiment the following dimensions have been found satisfactory:

' Inches Distance between pin 4 and outer end of knob '7 3.875 Distance between pins 4 and-14 1.657. Pitch diameter of member 11. 0.562 Pitch diameter of member'12.. 2.812

Eflective radius of pin 14 on member 12-.. 1.093

In this particular embodiment, a two-inch linear movement of the pointer l5 provided a rotation of the shaft 10 of the variable control 8 of approximately 315 degrees, the lever 3 moving through approximately 36 degrees.

While there has been described what is 'at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A variable-control actuating mechanism comprising a lever slidably pivoted at one end about an axis parallel to the shaft ofsaid vari-' first member mounted on said shaft, and an is controlled by the rheostat 21. When the slider arcuately shaped second member engaging said first member and being swivelly connected to said lever, said first and second members being so proportioned that rotation of said lever about its pivot through relatively few degrees produces rotation of said shaft through relatively many degrees.

3. A' variable-control actuating mechanism comprising a lever slidably pivoted at one end about an axis parallel to the shaft of said variable control, a first member mounted on said shaft, and anarcuately shaped second member I engaging said first member and being swivelly connected to said lever, said first and second members being so proportioned that rotation of tween the pivot 01 said lever and its pointofswivel being so proportioned with respect to the effective radius of said point of swivel on said second member that the free end of said lever" said lever about its pivot through relatively few 5 moves in a substantially straight line.

degrees produces rotation of said shaft throughrelatively many degrees, and the distance be- GEORGE WILLARD THELINL 

